The alkali feldspars from microsyenitic dylces of southern

• Main Authors: H. G. Scttarbert, Ph. D
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1966
• Subjects: Greenland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.608.3519; http://www.minersoc.org/pages/Archive-MM/Volume_35/35-275-903.pdf

Summary. 26 b-axis oscillation photographs of alkali feldspars of microsyenitic dykes of Southern Greenland are presented. The crystals are rather estricted in composition (Or42. ~ to 0r35.3) but are rather ich in Ca (up to 14 % An). The range of variation of the optic axial angles, 2V 45 ~ to 71 ~ (exceptions up to 87 ~ puts the crystals between sanidine-anorthoclase cryptoperthite and orthoclase microper-thite, as classified by Turtle (1952). Since the syenitic magma cooled own rather apidly some peculiarities in the structural state of the alkali feldspars are to be expected. The potassium-rich p ase is (nearly) monoclinic. According to the values of the reciprocal lattice angles a * and y * the sodium-rich phases can be divided into three groups: high-temperature pericline-twinned and high-temperature albite-twinned phases, high-tempera-ture pericline-twinned and low-temperature albite-twinned phases, and high-tem-perature perieline-twinned and low-temperature albibe-twinned phases with nearly identical values of the reciprocal lattice angle V*. I N 1938 Wegmann established the structural division of the Pre- cambrian of southern Greenland by introducing the concepts of